“There’s any number of reasons why a heater or defroster isn’t working. Sometimes they are simple fixes, other times they are indicative of larger problems,” said Steve Schaeber, manager of service training for the Mobile Air Conditioning Society.

The heating and cooling systems routinely feed off one another, so problems with one may affect the other.

Low coolant levels reduce the heater’s ability to warm the interior. Leaks in the heater core, hoses, radiator or cooling system will lead to a lack of coolant and create problems in the system.

A heater or defroster fails for one of three reasons, Schaeber said. There could be an electrical problem such as a blown fuse, an air flow problem within the ventilation system itself, or an issue with the vehicle’s cooling system (such as lack of antifreeze).

Experienced technicians can often spot problems with a visual inspection, though many modern cars also have specialized codes that can be deciphered by a diagnostic test.

Below, Schaeber outlines what could cause your heater or defroster to malfunction.

Ventilation problem. The lines could be clogged with leaves and twigs accumulated during summer and fall.

A problem with the electrical system. Have the fuses checked to potentially find the root of the issue.

The engine’s cooling system could be to blame. Make sure you have enough antifreeze and the system is functioning properly. Some problems can be diagnosed visually, while others require a diagnostic scan for trouble codes.